In the production of elastomers such as butyl, halobutyl or ethylene-propylene type rubbers (as well as other thermoplastic polymers), it is customary to pelletize the thermoplastic material by means of extruder-cutter arrangements. One type of such a cutter is generally referred to as a "turbulator". Several versions of such apparatus are described in U.S. Pat. Nos. assigned to Welding Engineers, Inc. (see, e.g. U.S. Nos. 4,465,451; 4,451,414; 4,446,094; 4,110,843; 3,917,507; and 3,874,835), as well as in U.S. Pat. No. 3,973,890 granted Aug. 10, 1976 to Porter et al. and U.S. Pat. No. 4,483,886 granted Nov. 20, 1984 to R.C. Kowalski. As is described in the Porter et al. '890 patent, a die plate associated with a thermoplastic extruder device is cylindrical in shape and is provided with radially extending extrusion orifices through which heat-plasticized material is extruded. A rotary feed screw is provided upstream of the die plate to pressurize the material and cause it to extend from the orifices in the plate. A rotating cutter is provided within the cylindrical opening in close proximity to the face of the die plate and acts to cut the rubber "crumb" as it is extruded. Air or other gas is introduced through the cutter blades within the cylindrical opening to cool, dry and transfer the dried rubber away from the extruder to the next step in the process.
In the Kowalski '886 patent, methods are disclosed for coating pellets of, for example, rubber by mixing coating material in a stream of carrier gas and contacting heated pellets of the rubber with the stream of gas and coating material so as to form a layer of melted coating on the pellets. Kowalski thus discloses techniques for conveying pellets of rubber and other materials in streams of carrier gases.
Additional turbulator apparatus for producing granulated particles is also described, for example, in U.S. Pat. No. 3,316,590 -- Rettig. Cutters for producing pellets of elastomeric material and pneumatic systems for dispersing pelletized material are also disclosed in U.S. Pat. No. 3,669,722 -- Bishop.
While the foregoing arrangements have been found to be generally satisfactory and, as noted above, a great deal of development work has been done by a number of investigators over a period of years on such apparatus and methods, it has been found that it is necessary to shut down and refurbish the equipment more frequently than is desirable. Furthermore, the apparatus includes components (such as large motors) which are relatively expensive, both in terms of original cost and operating costs. Still further, the rotary cutter arrangements, in the course of severing the crumb from the extrusion die produce more "fines" (small particles) than are desirable.
In addition, the formation at elevated temperature of such thermoplastic particles can result in those particles adhering to surfaces of the equipment and/or to one another, thereby requiring periodic cleaning and other maintenance.
It is therefore desirable to reduce the complexity, cost and maintenance problems encountered with such prior turbulator equipment and processes.